The significance of the invention is most easily described in relation to a turbine for a gas turbine engine. In order to obtain a high specific capacity in a turbine jet power plant such as a gas turbine engine to render it competitive with conventional internal combustion engines, it is necessary to operate the turbine engine at a comparatively high gas temperature such as 1,350.degree. C. At such temperatures it has been found undesirable to use metallic materials including those often called super-alloys for the turbines. Instead, techniques of turbine manufacture suggest the use of refractory (high-temperature resistant) ceramic material and, preferably, nonoxide ceramic materials such as those of the ceranox group which includes, particularly, Si.sub.3 N.sub.4 and SiC. U.S. Pat. No. 3,905,723 discloses a ceramic turbine made entirely from this kind of material.
Although the ceramic materials described are desirable for forming turbines, it is difficult to fasten turbines or other articles made from these materials to other structures such as a metallic turbine shaft. Until now, connections of this type could be made only with great difficulty.
The low coefficient of thermal expansion of the ceramic materials is one advantage of their use for turbines. This advantage, however, becomes a disadvantage when faced with the problem of connecting the turbine to a shaft with a different coefficient of thermal expansion.
The hardness of brittleness of the ceramic materials present further problems of connecting articles made therefrom to other structures. Special treatments which present particular risk of damage of the ceramic article and are costly have been required. Welded or soldered joints between the ceramic material and the other structure cannot be made because the ceranox or other ceramic materials are not receptive to welding or soldering operations.